1. Field of the Invention
The present invention relates to character generating systems and, more particularly, to a digital such system having a minimum data storage requirement and wherein character display controls are derived by computations on a few stored parameters by which each character is encoded.
2. State of the Prior Art
Character generators have numerous applications, a common commercial one being phototypesetters. Early such devices were primarily optical and used masks formed in the character configurations. CRT displays were developed wherein the patterns may be defined either optically or from digitally derived signals. As one example, a flying spot scanner is optically coupled to a matrix of character representations to derive the digital signals for the pattern in U.S. Pat. No. 3,324,346.
Other CRT systems have employed masks which are scanned for a similar purpose, as in U.S. Pat. Nos. 2,275,017 and 2,379,880.
One brute force method of character encoding is to identify each element or dot of a matrix of dots which correspond to the character segments when a character is superimposed on the matrix. A dot-type generating system is described in U.S. Pat. No. 3,165,145. A severe disadvantage of this approach is the excessively large amount of storage required for even moderate to poor quality reproduction.
Another form of coding developed in the prior art generally involves the breaking down of a character's area into narrow strips and quantizing and storing the starting coordinates and length of each strip. Such a technique is disclosed in U.S. Pat. No. 3,305,841. An improvement in that technique is set forth in U.S. Pat. No. 3,471,848 wherein an incremental form of encoding the terminal points of successive strips is employed. This generally serves to reduce the required memory for the encoded character data.
An alternative approach in the more recent prior art is set forth in U.S. Pat. No. 3,422,419 in which a set of characters is analyzed to define a plurality of patterns which are common to one or more characters and are of substantially rectangular configuration, comprising a plurality of line segments of controlled length. Each character is encoded as comprising a combination of selected ones of these common patterns. Such a system, while reducing storage requirements, can pose great restrictions on the font styles and result in some distortion of the generated characters.